1. Field of the Invention
This invention relates to a photo-taking lens and an optical apparatus, and more particularly to a zoom lens and an optical apparatus adapted for a video camera, a still camera, a surveillance camera, or the like.
2. Description of Related Art
Zoom lens optical systems adapted for optical apparatuses of the above-stated kinds have been variously arranged. In the case of the zoom lens optical system shown in FIG. 15, the system has a zoom lens barrel of a type composed of four lens groups in which the fourth lens group disposed rearmost in the zoom lens barrel is used for focusing. The zoom lens barrels of this type are most popularly used in the field of video cameras.
Referring to FIG. 15, the four component lens groups of the zoom lens barrel include a fixed front lens group 111, a variator lens group 112, a fixed lens group 113 and a focusing (compensator) lens group 114. A guide rod 133 is arranged to prevent turning of the variator lens group 112. A feed rod 134 is arranged to feed the variator lens group 112. A fixed lens tube 135 is arranged to support the fixed front lens group 111, the guide rod 133 and the feed rod 134. An iris unit 136 is inserted in the lens barrel (perpendicularly to the paper surface as viewed in the drawing). A stepping motor 137 is arranged to serve as a focusing motor. The stepping motor 137 has an output shaft 138. The output shaft 138 is provided with a male screw 138a formed thereon for moving the focusing lens group 114. The male screw 138a is in mesh with a female screw part 139 which is formed integrally with a moving frame 140 of the focusing lens group 114.
Guide rods 141 and 142 are arranged to guide the focusing lens group 114. A rear plate 143 is arranged to position and retain in place the guide rods 141 and 142. The zoom lens barrel further includes a relay holder 144, a zoom motor 145, a reduction gear unit 146 for the zoom motor 145, and interlocking gears 147 and 148. The interlocking gear 148 is secured to the feed rod 134 which is provided for the variator lens group 112.
The zoom lens barrel operates as follows. When the stepping motor 137 acts to drive, the focusing lens group 114 is moved by screw feeding in the direction of an optical axis. When the zoom motor 145 acts to drive, the feed rod 134 is caused to rotate through the interlocking gears 147 and 148. The rotation of the feed rod 134 causes the variator lens group 112 to be moved also in the direction of the optical axis by a lens frame 112a which is screw-coupled with the feed rod 134.
FIG. 16 shows positional relations obtained in the above-stated zoom lens barrel between the variator lens group and the focusing lens group at some of different object distances. This drawing shows, by way of example, the positional relations obtained in focusing at object distances including an infinity distance, 2 m, 1 m, 80 cm and 0 cm. In a case where the zoom lens barrel is of an inner-focus type, the positional relation between the variator lens group and the focusing lens group varies with the object distance. Therefore, unlike a zoom lens barrel of a front-lens-focus type in which lens groups are moved by a mechanical arrangement such as a cam ring, a defocused state would result from a mere driving action of the zoom motor 145 alone in the case of the zoom lens barrel which is arranged as shown in FIG. 15.
To solve this problem, the positional relation between the variator lens group and the focusing lens group as shown in FIG. 16 must be controlled to optimize it according to the object distance. As such a control, for example, in Japanese Laid-Open Patent Application No. HEI 1-280709 and Japanese Laid-Open Patent Application No. HEI 1-321416, there is disclosed a method for tracing the locus of the positional relation between a variator lens group and a focusing lens group which varies with the object distance.
FIG. 17 shows in a block diagram an arrangement for carrying out the above-stated locus tracing method. Lens groups 111 to 114 are the same lens groups shown in FIG. 15. The position of the variator lens group 112 is detected by a zoom encoder 149. The zoom encoder 149 may be, for example, a volume encoder having a brush mounted on a variator moving ring in one body therewith and arranged to slide over a circuit board having a printed resistance pattern.
An iris encoder 150 is arranged to detect an aperture value of the iris unit 136 by using, for example, the output of a Hall element 163 disposed within an iris meter. An image sensor 151 is composed of a CCD or the like. A camera signal processing circuit 152 is arranged to output a Y signal, which is supplied to an AF circuit 153. Upon receipt of the Y signal, the AF circuit 153 makes a discrimination between an in-focus state and a defocused state. In the event of a defocused state, the AF circuit 153 checks it to find if it is a front-focus state or a rear-focus state and also to find a defocused degree. The results of the checks are sent to a CPU 154.
A power-on reset circuit 155 is arranged to be used in performing various resetting action when a power supply is turned on. A zoom operation circuit 156 is arranged to supply the CPU 154 with information on the details of an operation performed on a zoom switch 157 when the zoom switch 157 is operated by the operator. Memory parts 158, 159 and 160 are arranged to store data relative to loci which correspond to different object distances as shown in FIG. 16. The memory part 158 stores direction data. The memory part 159 stores speed data. The memory part 160 stores boundary data.
A zoom motor driver 161 is arranged to drive the zoom motor 145. A stepping motor driver 162 is arranged to drive the stepping motor 137 by applying input pulses to the stepping motor 137. The number of input pulses applied to the stepping motor 137 is continuously counted by the CPU 154. The count number thus obtained is used as an encoder for the absolute position of the focusing lens group 114.
With the zoom lens barrel arranged in this manner, the position of the variator lens group 112 and that of the focusing lens group 114 are determined respectively by the zoom encoder 149 and the number of input pulses applied to the stepping motor 137 so as to decide one point on a map shown in FIG. 16.
The map shown in FIG. 16 is divided by means of the boundary data 160 into small rectangular areas I, II, III, - - - as shown in FIG. 18. In FIG. 18, hatched parts represent inhibiting areas where the lens groups 112 and 114 cannot be set. With one point decided as described above, it is possible to detect in which of the small areas the point is located.
The speed data part 159 and the direction data part 158 respectively store the speed and the direction of rotation of the stepping motor 137 obtained from a locus passing the center of each of these areas. In the case of FIG. 18, for example, an abscissa axis which indicates the positions of the variator lens group 112 is divided into 10 zones. Assuming that the speed of the zoom motor 145 is set to move the variator lens group 112 from a telephoto end position to a wide-angle end position in 10 seconds, the variator lens group 112 passes each of these zones in one second.
Referring to FIG. 19 which shows the area III of FIG. 18 in an enlarged state, a locus 164 passes through a middle part of the area III. A locus 165 passes through a lower left part of the area III. A locus 166 passes through an upper right part of the same area. These loci have inclinations which differ a little from each other. The illustration indicates that the middle focus 164 can be accurately traced without much error if the focusing lens group is caused to move at a speed of x mm/second.
Assuming that the speed obtained in this manner is called an area representative speed, the speed data memory part 159 stores, for each area, as many values of the area representative speed as the number of the small areas. With this area representative speed assumed to be indicated by an arrow 168, the speed of the stepping motor 137 is set by finely adjusting the area representative speed as indicated by arrows 167 and 169 on the basis of detection results obtained by an automatic focus adjusting device. As for the direction data memory part 158, since the rotating direction of the stepping motor 137 varies according to the area even in the case of zooming from the telephoto end position to the wide-angle end position and vice versa, sign data is also stored in this memory part 158.
As mentioned above, the speed of the stepping motor 137 is obtained by correcting the area representative speed which is obtained according to the position of the variator lens group 112 and that of the focusing lens group 114 and by further correcting the area representative speed according to the result of detection made by the automatic focus adjusting device. With this speed used for controlling the position of the focusing lens group by driving the stepping motor 137 while the zoom motor 145 is in process of driving, even the zoom lens of the inner-focus type can be adequately kept in focus even during the process of zooming.
According to another method, three speeds including speeds indicated by the arrows 167 and 169 in FIG. 19 in addition to the above-stated area representative speed indicated by the arrow 168 are stored for each of the areas and selected according to the result of detection made by the automatic focus adjusting device.
Other methods hitherto employed include a method whereby a locus passing through a point decided on the map from the current positions of the variator lens group and the focusing lens group is computed and is used to be traced, and another method whereby a plurality of loci are stored beforehand as positions of the focusing lens group according to positions of the variator lens group.
In the case of Japanese Laid-Open Patent Applications No. HEI 1-321416, positions of the focusing lens group for a plurality of positions of the variator lens group between the wide-angle end position and the telephoto end position are stored beforehand. At the commencement of zooming, a point on the map determined by the current position of the variator lens group and that of the focusing lens group is detected. Then, an interpolating computing operation is carried out using stored data of points located nearest to the detected point on front-focus and rear-focus sides. After the interpolating operation, the position of the focusing lens group is computed for each focal length (position of the variator lens group).
FIG. 20 shows a locus of the positions of the focusing lens group obtained in the neighborhood of the telephoto end of a zooming range. According to the disclosure of the Japanese Laid-Open Patent Application No. HEI 1-321416, information on the data stored includes focusing lens group positions rr1, rr4, rr7 and rr9 which are represented by a locus LL1 for the variator lens group positions Vn (telephoto end position), Vn-1, Vn-2 and Vn-3. In other words, a locus passing through points P1, P4, P7 and P10 of the map is stored as an .infin. locus.
The stored data also includes, for the variator lens group positions Vn (telephoto end), Vn-1, Vn-2 and Vn-3, information on the focusing lens group positions rr2, rr5, rr8 and rr10 which are represented by a locus LL2 and stored, for example, as a focusing locus for 10 m. Data is of course prepared in this manner to cover the whole zooming range from the telephoto end to the wide-angle end.
In zooming from the position (Vn, rr), i.e., a point P within the map, points PA, PB and PC are obtained by an interpolating computing operation on the basis of the data stored for a variator lens group position nearest on the front (near) focus side, i.e., the data of the locus LL2 and the data stored for a variator lens group position nearest on the rear (far) focus side, i.e., the data of the locus LL1. The focusing lens positions are obtained for focal length positions V0 (wide-angle end), V1, V2, - - - - Vn-1, Vn (telephoto end) to determine a locus during the process of zooming.
Since the points PA, PB and PC are obtained by the interpolating computing operation, a ratio of a distance between the points P1 and P to a distance between the points P2 and P becomes, for example, equal to a ratio of a distance between the points PA and P4 to a distance between the points PA to P5.
A memory relative to speeds or a memory relative to positions is thus prepared of course on the basis of optical design values on the assumption that the lens barrel is manufactured with no manufacturing error.
Each of embodiments of this invention which will be described later herein is an inner-focus type zoom lens composed of four lens groups of positive-negative-positive-positive refractive power arrangement like the lens barrel of the prior art described by way of example above. In the lens group arrangement, the second lens group is a variator lens group and the fourth lens group is a focusing lens group. However, this invention is applicable also to lens barrels of different arrangements, for example, such as the one disclosed in FIGS. 5, 7 and 8 of Japanese Laid-Open Patent Application No. HEI 3-27011.
In the case of the prior art described above, a DC motor having a gear head is employed as a zoom actuator. However, a stepping motor may be employed like the actuator of the focusing lens group (the fourth lens group). In that case, the absolute position of the variator lens group (the second lens group) is preferably detected by means of counting the number of input pulses indicating a reference reset position in the same manner as the means employed for the focusing lens group, instead of the use of a volume encoder mentioned in the foregoing.
In the prior art example described above, the zooming intention of the operator is imparted by an operation on the zoom switch 157 shown in FIG. 17. In a case where a zooming speed is to be changed, the speed may be changed by detecting, for example, an amount to which the zoom switch 157 is pushed (pushing amount).
In most cases, a zoom switch, such as the above-stated one, is preferably disposed within an easy reach of an operating finger. Therefore, in the case of a relatively compact video camera adapted for use by general consumers, the zoom switch is disposed on the side of the camera body, for example, as shown in FIG. 21.
If a zooming operation is to be controlled solely by means of the zoom switch 157, the variator lens group (the second lens group) cannot be moved directly by the operator. Therefore, in the case of the optical system described above, the CPU 154 must be arranged to act to control the second and fourth lens groups in such a way as to cause the fourth lens group to move adequately in relation to the movement of the second lens group.
In order to have the variator lens group not moved directly by the operator, on the other hand, there is a limit in respect of the zooming speed. In a case where a stepping motor is used as the second lens group driving means (the zoom motor) 145 while a stepping motor is also used for the fourth lens group driving means (focusing motor) 137, at least a period of time of 2 to 3 seconds has been necessary in general in moving the lens groups from the telephoto end to the wide-angle end, depending on the magnifying rate of zooming, the characteristic of each of the motors, a lead pitch, etc.
The zooming operation of the inner-focus type zoom lens composed of four lens groups and generally employed at present is as described above.
A front-lens focusing type zoom lens which is arranged to use the first lens group for focusing is next described. FIG. 22 shows a manner generally employed in arranging a front-lens focusing type zoom lens.
Referring to FIG. 22, the zoom lens is composed of a first lens group 2101 which is a focusing lens group, a variator lens group 2102, a compensator lens group 2103 and a relay lens group 2104. The zooming lens includes a fixed lens tube 2105, a female helicoid tube 2106, a front lens tube 2107, a relay holder 2108, a relay lens tube 2109, an iris blade unit 2110, an iris motor 2111, a zoom motor body 2112, a zoom motor gear head part 2113, a focus motor body 2114, a focus motor gear head part 2115, a focus motor output gear 2117, a gear part 2118 formed integrally with the female helicoid tube 2106, a zoom ring 2119, a gear part 2120 formed on the zoom ring 2119 integrally therewith, a projection 2121 provided for transmitting the rotation of the zoom ring 2119 to a cam ring 2122, the cam ring 2122, a cam groove 2123 provided in the cam ring 2122 for the variator lens group, a cam groove 2124 provided in the cam ring 2122 for the compensator lens group 2103, a variator moving ring 2125, a compensator moving ring 2126, a cam follower part 2127 formed integrally with the variator moving ring 2125, a cam follower part 2128 formed integrally with the compensator moving ring 2126, guide rods 2129 and 2130 which are provided for the moving rings 2125 and 2126, a focus motor slip unit 2131, and a zoom motor slip unit 2132.
During focusing in the front-lens focus type zoom lens, the focusing lens group 2101 is moved in the direction of an optical axis. For this purpose, the focusing lens group 210 (the first lens group) 2101 is secured to the front lens tube 2107. The outside diameter of the front lens tube 2107 is arranged to be fitted into the inner diameter of the female helicoid tube 2106 without play and to be fixed in place with an adhesive after adjusting its position in the direction of the optical axis. The female helicoid tube 2106 engages the fixed lens tube 2105 through its helicoid screw. Therefore, the focusing lens group 2101 can be moved in the direction of the optical axis by rotating the female helicoid tube 2106.
In the case of the front-lens focus type zoom lens, the focusing lens group is arranged in front of the variator lens group (the second lens group) and the compensator lens group (the third lens group). The lens arrangement enables the operator to directly move the variator lens group for zooming at any suitable speed without causing any change in focus.
The operations of zoom lenses of two different types, i.e., the inner focus type and the front-lens focus type, have been described above. The inner focus type generally permits more reduction in size than the front-lens focus type to permit reduction in cost and energy. Further, with regard to the lens barrel mechanism, the front-lens focus type requires use of many parts of complex shapes which makes it difficult to ensure an adequate degree of precision for such parts.
In view of these advantages, a lens barrel of the inner focus type has variously been arranged to increase a maximum lens group moving speed by using a linear actuator for a high speed zooming and also for removal of noises and vibrations caused by a stepping motor. FIGS. 23(A) and 23(B) show one example of such an arrangement. In the case of FIGS. 23(A) and 23(B), a voice coil motor of the moving coil type is employed as the linear actuator. FIG. 23(B) is a longitudinal section taken on a line B--B of FIG. 23(A). Referring to FIGS. 23(A) and 23(B), a yoke 1117a and a coil 1116 which is wound around a bobbin 1119 are arranged on the outer circumferential side of a lens holding frame 1111 which is arranged to hold lenses 1101b1 to 1101b3. To the yoke 1117a is opposed a yoke 1117b which is located outside of the coil 1116. A magnet 1115 is bonded to the yoke 1117b. The yokes 1117a and 1117b and the magnet 1115 are mounted on a fixed tube 1102. The lens holding frame 1111 is carried by two parallel guide rods 1103a and 1103b to be movable in the direction of an optical axis 1105.
The magnet 1115 is magnetized as shown in FIG. 23(B). Therefore, a magnetic field is formed between the yokes 1117a and 1117b in the radial direction. The coil 1116 is located between the yokes 1117a and 1117b and is wound in the circumferential direction. When a current is allowed to flow through the coil 1116, a driving force is generated for driving in the direction of the optical axis. The lens holding frame 1111 and the lens groups 1101b1 to 1101b3 which are arranged integrally with the bobbin 1119 are then driven in the direction of the optical axis. The voice coil type actuator which has been described may be differently arranged in various manners. Further, it is also conceivable to use a motor operating on some different principle, such as an ultrasonic motor.
While various zooming lens arrangements have been described in detail above, there has been known a method of attaining a zooming effect called "electronic zoom". According to the "electronic zoom" method, while the size of an image formed on an image forming plane remains unchanged, an image range to be actually recorded or outputted can be caused to gradually vary on the image forming plane.
The electronic zoom method corresponds to the conventional enlargement photography whereby an image is enlarged by trimming. The electronic zoom method thus has a disadvantage in that the quality of picture deteriorates to a greater degree accordingly as the image position is located closer to the telephoto end (accordingly as the cutting range becomes narrower). The electronic zoom is, therefore, inferior to optical zooming. However, the advancement of various methods for interpolating video signals has come to enable electronic zooming to enlarge images up to about two magnifications in a state acceptable for practical applications.
For example, assuming that a video camera for general consumers, shown in FIG. 21, has a zoom lens of 12 magnifications and an electronic zooming power of two magnifications, a zooming effect of 24 magnifications is obtainable in all. In such a case, when the zoom switch 157 is operated to zoom from the wide-angle end toward the telephoto end, a zooming action is carried out by combining the electronic zoom with the optical zoom after the variator lens group arrives at the telephoto end position of the optical zoom, as shown in FIGS. 8(A) to 8(C).
In FIG. 8(A), the abscissa axis shows a period of time for which the zoom switch 157 is being pushed, while the ordinate axis shows the magnifying rate. After arrival of the variator lens group at the telephoto end position as shown in FIG. 8(B), the electronic zoom comes to cause the magnifying rate to continuously increase. The magnifying rate of the optical zoom varies in a manner as shown in FIG. 8(C).
While FIGS. 8(A) to 8(C) show changes in position on the assumption that all the positional changes linearly take place, the changes do not have to linearly take place. Further, the point of change-over from the optical zoom to the electronic zoom is arranged to be one point at the telephoto end. However, it is conceivable to arrange the optical zoom and the electronic zoom to have some overlapping area.
It is known to arrange a camera to interchange with each other the lenses of the varied kinds described.
FIG. 24 shows in a block diagram the arrangement of a system for interchangeable lenses. In the case shown, a zoom lens which is composed of four lens groups is used. These lens groups are arranged in a manner most popularly employed for a video camera to have refracting powers in the order of positive, negative, positive and positive refracting powers. The zoom lens is, however, not limited to this lens arrangement.
Light from an object comes through a first lens group 111 which is fixed, a variator lens group 112 which is a second lens group arranged to perform a magnification varying action, an iris 136, a third lens group 113 which is fixed and a focusing lens group 114 which is a fourth lens group arranged to perform a focus adjusting function and also a compensating function for correcting any shift of a focal plane resulting from the changes taking place during variation of magnification. The three primary color components, i.e., red, green and blue components, of the light passing through these lens groups are imaged respectively on image sensors 303 to 305 which are composed of CCDs or the like.
The images formed on the image sensors 303, 304 and 305 are photo-electrically converted and amplified to an optimum level by amplifiers 405, 406 and 407. Each of the amplified images is inputted to a camera signal processing circuit 152. The image is then converted into a standard television signal and, at the same time, is read out in the form of data by a microcomputer 409 (camera microcomputer) disposed in a camera body 419 as information on automatic focusing and automatic exposure adjustment.
The information (or data) read out by the camera microcomputer 409 is transmitted together with information on the state of operation switches of varied kinds such as a zoom switch, etc., disposed on the side of the camera body 419 to a lens microcomputer 410 through a contact 307 disposed on the side of the camera body 419 and a contact 318 disposed on the side of a lens unit 418. The lens microcomputer 410 carries out a motor control program on the basis of the information of varied kinds sent from the camera microcomputer 409 for automatic focusing (focus adjustment) The focusing lens group 114 is moved in the direction of an optical axis for focusing by driving a focus motor 137 through a motor driver 162.
Further, in a case where information on the state of the zoom switch sent from the camera microcomputer 409 calls for an action to keep a focal plane in place while zooming is in process, the lens microcomputer 410 carries out the focal plane keeping action by giving signals to a zoom motor driver 161 and the focus motor driver 162 on the basis of data of positions which is stored within the lens microcomputer 410 as data necessary for maintaining an in-focus state according to each of various object distances.
In accordance with the signals from the lens microcomputer 410, the zoom motor driver 161 and the focus motor driver 162 respectively drive the zoom motor 145 and the focus motor 137. The variator lens group 112 and the focusing lens group 114 are thus moved in the direction of the optical axis, so that a zooming action can be carried out without changing a focus position.
Further, the lens microcomputer 410 is arranged to give a signal for an apposite exposure to an iris driver 414 on the basis of information on the exposure adjustment coming from the camera microcomputer 409 and information from an encoder 163 which is provided for detecting the aperture state of the iris 136. Then, in accordance with the signal from the lens microcomputer 410, the iris driver 414 drives an actuator 413 to stop down the aperture of the iris 136 for an apposite exposure.
The contacts 307 and 318 are arranged both on the camera body side and on the lens side to be detachably interconnected to permit communication between the camera microcomputer 409 and the lens microcomputer 410. The lens unit 418 thus can be detachably mounted on the camera body 419. The arrangement enables the camera to carry out all actions for automatic focusing, automatic exposure adjustment and zooming without any problem in the same manner as an ordinary video camera for which a lens and a camera body are arranged in one body.
In the camera system of such an interchangeable lens type, a communication route is formed through the contact of the contacts provided for the lens and camera microcomputers 410 and 409. The details of this are as shown in FIGS. 25 and 26. FIG. 25 shows in a sectional view the lens barrel in a state of being mounted on the side of the camera shown as an optical apparatus. FIG. 26 shows an end face of the lens barrel as viewed before it is mounted on the camera. The camera is assumed to be a so-called 3 CCD video camera arranged to have three prisms for obtaining an image by color-separating the image into three colors of R (red), Green (G) and blue (B). However, the camera may be of some other different type.
The camera is provided with a color separation prism 302, a base member 301 which is arranged to carry the color separation prism 302, and a mount member 306 (which is assumed to be a bayonet mount in this case but may be some other tightening mount) for interchangeable lenses. The camera is provided also with the CCDs 303, 304 and 305 and the electrical contact 307. The electrical contact 307 is arranged to permit communication between the camera microcomputer 409 and the lens microcomputer 410 for automatic-focusing and automatic-iris-control functions.
On the side of the lens unit 418, four movable lens groups 311 to 314 are arranged in the rearmost part of the lens unit 418. These lens groups are movable in the direction of the optical axis and are integrally secured to a moving tube 315. The moving tube 315 has a sleeve part 316 and is arranged to be movable in the direction of the optical axis, for example, with the sleeve part 316 being positioned by a metal pole member 400. Although they are not shown, various actuators described by way of example in the foregoing description of the conventional arrangement example are arranged to move the lens groups in the direction of the optical axis.
The movable lens groups 311 to 314 are arranged within a fixed tube which is not shown. A mount part 308 is arranged at the rear end of the fixed tube to form a bayonet mount on the lens side. Further, the mount part 308 is arranged to have the lens correctly positioned in mounting it in conjunction with the mount part 306 which is disposed on the side of the camera body 419. A contact 318 is arranged on the lens side to be in contact with the contact 307 of the camera body for communication between the lens unit 418 and the camera body 419 when the lens unit 418 is mounted on the camera body 419.
A glass holder 309 having a flat glass plate 310 is secured from behind to the lens side mount part 308 by means of a claw part 317. When the lens unit 418 is removed from the camera body 419, the operator may touch the flat glass plate 310 but the movable lens groups are effectively prevented from being touched by the operator.
A zooming action of an inner-focus type zoom lens, a zooming action of a front-lens focusing type zoom lens, an electronic zoom action, and a method for interlocking the optical zoom with the electronic zoom, an interchangeable lens system, and the arrangement of contact parts for mounting an interchangeable lens, in an optical apparatus such as a video camera, a still camera, a surveillance camera or the like, have been described in detail above.
According to the arrangement of the inner focus type zoom lens described above, it is hardly possible with the zoom switch 157 shown in FIG. 21 to finely and quickly set the angle of view even if the lens is arranged to permit zooming at a high speed. Therefore, it has been desired to arrange the inner focus type zoom lens to permit a zooming operation by rotating a ring around the optical axis of the lens in the same manner as in the case of the front-lens focusing type zoom lens.
Further, in the case of an interchangeable lens system having the electronic zoom function on the side of the camera body, the lens has presented the following problem.
A method for zooming, particularly, a method for interlocking the electronic zoom with the optical zoom, when (i) a photo-taking lens of the kind enabling the operator to directly move the variator lens group or (ii) a photo-taking lens of a kind other than the kind (i) is mounted on the camera, has not been clearly disclosed. As a result, the second lens group (the variator lens group) of the lens might be moved toward the wide-angle end while the electronic zoom still remains in an on-state. Under such a condition, a shooting operation would be carried on with the electronic zoom left in the on-state, which deteriorates the picture quality, although the shooting could be carried on to obtain a better picture quality at the same angle of view by using some other combination of the magnifying rate of the optical zoom and the magnifying rate of the electronic zoom.